1. Field of the Invention
The present invention relates to a semiconductor light-emitting element, a fabrication method thereof, a convex part formed on a backing, and a convex part formation method for the backing.
2. Description of the Related Art
As a semiconductor laser characterized by a low threshold current Ith, a semiconductor laser having a separated double-heterojunction (SDH) structure and being cable to be formed in the course of one epitaxial growth process (hereinafter, referred to as an SDH semiconductor laser) is known owing to, for example, U.S. Pat. No. 2,990,837 (patent document 1).
As for the SDH semiconductor laser, first, a convex part that extends in the direction of a {110} A face is formed on an element fabrication substrate having a {110} face as the principal surface thereof. When crystal growth is induced on the principal surface of the element fabrication substrate, a light-emitting portion is formed on the {100} face that is the top surface of the convex part while having compound semiconductor layers accumulated thereon. The light-emitting portion has such a structure that a first compound semiconductor layer exhibiting a first conductivity type, an active layer, and a second compound semiconductor layer exhibiting a second conductivity type are sequentially accumulated. Assuming that the light-emitting portion is cut along a virtual plane (equivalent to the {110} face) in a direction perpendicular to the direction in which the convex part extends, the sectional shape is, for example, an isosceles triangle. The flank (slope) of the light-emitting portion is formed with a {111} B face. In general, according to the metal organic chemical vapor deposition (MOCVD) method (which may be referred to as the metal organic vapor phase epitaxy (MOVPE) method), the {111} B face is known as a non-growth face, though it may not be under a special condition for crystal growth. Therefore, as long as the SDH semiconductor laser is concerned, once the light-emitting portion whose flank is the {111} B face is formed, even if MOCVD is continued, the crystal growth of the light-emitting portion is retained in a self-growth suspended stage. Herein, the inclination (θ111B) of the {111} B face is 54.7°.
Incidentally, in this specification, the notation (hkl) denotes a crystal face. Herein, a negative integer is written with a minus sign like (hk−l) but not written with a bar like (hk l). In addition, the notation of [hkl] denotes a direction. Herein, a negative integer is written with a minus sign like [hk−l] but not written with a bar like [hk l].
On part of the principal surface of the element fabrication substrate except the convex part (for convenience' sake, referred to as a concave-part surface) which has the {100} face, since a non-growth surface does not exist, if MOCVD is continued, compound semiconductor layers that crystallographically grow from the concave-part surface will soon fully bury the light-emitting portion whose self-growth is suspended. The compound semiconductor layers having crystallographically grown from the concave-part surface are structured to have a current block layer position adjustment layer, a current block layer, and a buried layer sequentially formed on the second compound semiconductor layer. Herein, at an intermediate step before the compound semiconductor layers that crystallographically grow from the concave-part surface bury the light-emitting portion (in particular, when the compound semiconductor layer reaches the vicinity of the side surface of the active layer included in the light-emitting portion), if the current block layer is formed by controlling the thickness of the current block layer position adjustment layer, a structure in which a current can be injected into the active layer alone of the light-emitting portion can be realized.
As mentioned above, in the SDH semiconductor laser, the compound semiconductor layers can be formed in the course of one crystal growth process. In addition, if a material whose energy band gap is larger than that of the active layer, that is, a material whose refractive index is low is selected as a material to be made into the compound semiconductor layers that up and down sandwich the active layer within the light-emitting portion (first and second compound semiconductor layers) or a material to be made into the current block layer, buried layer, or the current block layer position adjustment layer located outside the light-emitting portion, the active layer can be fully enclosed by the compound semiconductor layer that is preferred for light confinement. Eventually, a shape of a beam emitted from the semiconductor layer having the end surface of the convex part as a light emitting surface thereof can be approached to a real circle. In other words, θ// will be approximately equal to θ⊥ in a far-field pattern (FFP).
Otherwise or for example, depending on a lens coupling efficiency, the shape of a beam to be emitted from the semiconductor laser is requested to be elliptic. In this case, for example, a so-called flare stripe structure having the width near the end surface of the convex part expanded is adopted (refer to, for example, U.S. Pat. No. 3,399,018 (patent document 2)), whereby the θ// value in the FFP can be controlled to be small. In addition, the adoption of the flare stripe structure makes it possible to achieve a high-power light output.